MAGMO: polarimetry of 1720-MHz OH masers towards southern star-forming regions

Abstract

From targeted observations of ground-state OH masers towards 702 Multibeam (MMB) survey 6.7-GHz methanol masers, between Galactic longitudes 186 • through the Galactic centre to 20 • , made as part of the 'MAGMO' project, we present the physical and polarisation properties of the 1720-MHz OH maser transition, including the identification of Zeeman pairs. We present 10 new and 23 previously catalogued 1720-MHz OH maser sources detected towards star formation regions. In addition, we also detected 16 1720-MHz OH masers associated with supernova remnants and two sites of diffuse OH emission. Towards the 33 star formation masers, we identify 44 Zeeman pairs, implying magnetic field strengths ranging from −11.4 to +13.2 mG, and a median magnetic field strength of |B LOS | ∼ 6 mG. With limited statistics, we present the in-situ magnetic field orientation of the masers and the Galactic magnetic field distribution revealed by the 1720-MHz transition. We also examine the association statistics of 1720-MHz OH SFR masers with other ground-state OH masers, excited-state OH masers, class I and class II methanol masers and water masers, and compare maser positions with mid-infrared images of the parent star forming regions. Of the 33 1720-MHz star formation masers, ten are offset from their central exciting sources, and appear to be associated with outflow activity.

Turbulent dynamo in the two-phase interstellar medium

“…In the nearby spiral galaxy, M51, the large-scale radio polarisation observations, which probe the hot (and warm), diffuse phase of the ISM, show different magnetic field properties (especially the magnetic field structure) than that seen via the recent large-scale far-infrared polarisation observations, which probe the cold, dense phase (Fletcher et al 2011;Borlaff et al 2021). In the Milky Way, comparison between the large-scale magnetic field properties inferred from OH masers (a probe of the colder regions) to that from pulsars (a probe of warmer regions) are different (Ogbodo et al 2020). Even on the smaller scales in the Milky Way, magnetic fields in the warm and cold medium can be different (Campbell et al 2021).…”

SPLASH: The Southern Parkes Large-Area Survey in Hydroxyl -- Data Description & Release

“…Figure 14 plots the brightness temperatures of the satellite lines on a voxel-by-voxel basis, excluding high-gain masers. Known masers were removed using the catalogues of Qiao et al (2016Qiao et al ( , 2018Qiao et al ( , 2020 and Ogbodo et al (2020), and the unpublished catalogue of Ogbodo et al (in prep) 4 . The datapoints are colour coded by the 1666 MHz continuum brightness temperature at the location of the voxel, and by the 'velocity extent' of its parent spectral feature, defined as the number of contiguous channels over which the sense of the emission/absorption remains unchanged.…”

A Comparison of Multi-Phase Magnetic Field Tracers in a High-Galactic Latitude Region of the Filamentary Interstellar Medium

“…For instance, the polarization horizon of LOFAR is significantly closer than that of GALFACTS and may not sample the full polarizedemitting Galactic volume. More recently, Ogbodo et al (2020) compared magnetic field strengths derived using OH masers as part of the Mapping the Galactic Magnetic field through OH masers (MAGMO) project (Green et al 2012) to pulsar Faraday rotation measurements collated from Nota & Katgert (2010). These measurements probe the neutral and ionized medium, respectively, and were chosen toward H ii regions that should dominate the environment in both tracers.…”